Fixation and stabilization of metals in contaminated materials

ABSTRACT

The present invention discloses a method of treating lead bearing process materials and lead toxic hazardous wastes. The invention relates to treatment methods employed to chemically convert leachable lead in lead bearing solid and liquid waste materials to a non-leachable form by mixing the material with lime, gypsum and/or phosphoric acid. The solid and liquid waste materials include contaminated sludges, slurries, soils, wastewaters, spent carbon, sand, wire chips, plastic fluff, cracked battery casings, bird and buck shots and tetraethyl lead contaminated organic peat and muck. The present invention discloses a process comprising a single step mixing of one or more treatment additives, and a process comprising a two step mixing wherein the sequence of performing the steps may be reversible. The present invention provides a new way of treating a universe of lead contaminated materials at any pH.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.08/031,461, filed Mar. 15, 1993, which is a continuation-in-part of U.S.patent application Ser. No. 07/721,935, filed Jul. 23, 1991, now U.S.Pat. No. 5,193,936, continuation-in-part of U.S. patent application Ser.No. 07/494,774, filed Mar. 16, 1990, abandoned.

FIELD OF THE INVENTION

The present application describes treatment methods for metal-bearingmaterials, especially lead-bearing materials, such as process streams,sludges and slurries, including all types of liquid and solid wastes.

BACKGROUND OF THE INVENTION

Only a few prior art patents have taught the immobilization of lead indifferent kinds of wastes to make the treated residuals suitable fordisposal as special waste in a RCRA approved and licensed landfillfacility. For example, some known methods to treat broader groups ofmetals are shown in U.S. Pat. No. 4,149,968 to Kupiec et al., U.S. Pat.Nos. 4,889,640 and 4,950,409 to Stanforth, U.S. Pat. No. 4,701,219 toBonee, U.S. Pat. No. 4,652,381 to Inglis, and U.S. Pat. No. 4,671,882 toDouglas et al.

Kupiec et al. teaches the immobilization of heavy metals by treating analkaline slurry of waste with a mixture of bentonite clay and PortlandCement.

Stanforth teaches a method of treating solid hazardous waste (containingunacceptable levels of lead and cadmium) with reactive calciumcarbonate, reactive magnesium carbonate and reactive calcium magnesiumcarbonate. The patent teaches that addition of water is beneficial tofacilitate the mixing of the solid waste with treatment additive andconversion of lead into non-leachable forms. Stanforth further disclosesmixing solid waste with lime and carbon dioxide or bicarbonate.

Bonee discloses that calcium chloride, calcium carbonate, gypsum andsodium carbonate are relatively ineffective at reducing the leaching ofvanadium and nickel from a petroleum cracking process particulate waste.

Douglas et al. discloses a process for producing a nonhazardous sludgefrom an aqueous solution by addition of phosphoric acid or an acidphosphate salt, adjusting the Ph to about 5, adding a coagulatingpolymer and raising the Ph to above 7 through the addition of lime.Then, the process includes dewatering the resulting sludge. Thisconstitutes at least 5 or more steps making it cumbersome, timeconsuming and expensive.

Inglis teaches a process of treating industrial wastewater which has apH of 2 and which is contaminated with sulfuric acid, lead, copper andzinc. Calcium carbonate is added along with air to wastewater. Thisresults in neutralization and formation of insoluble metal salts. Theprocess is not applicable to wastes that have a pH of 6 to 9. However,limestone is relatively ineffective in removing lead from hazardous,solid or sludge material. Limestone does not react in the solidmaterials and metal carbonates that are formed are subject todegradation by acid and acidic landfill leachate conditions.

Hazardous wastes containing excessive amounts of leachable lead arebanned from land disposal. The regulatory threshold limit under ResourceCons. and Recovery Act is 5 mg/l of leachable lead as measured by TCLP(toxicity characteristic leaching procedure) test criteria, UnitedStates Environmental Protection Agency (USEPA) method 1311 (SW-846).Waste materials containing TCLP lead levels in excess of 5 mg/l aredefined as lead-toxic hazardous waste and are as such restricted fromlandfilling under current land ban regulations. The cost of disposinglead toxic hazardous waste materials in excess of $200.00 per ton plusthe cost of transporting the hazardous material to landfills forhazardous wastes, which do not exist in every state. This makes thedisposal of lead toxic hazardous waste materials very expensive.Therefore, treating the lead-bearing process materials and waste streamsto render them non-hazardous by RCRA definition would cut down the costsof transportation and disposal tremendously.

SUMMARY OF THE INVENTION

The present invention discloses a method of treating metal-bearing,especially lead-bearing process materials and lead-toxic hazardouswastes.

The present invention relates to a chemical treatment technology forimmobilizing leachable lead in contaminated soils and solid wastematerials. According to the present invention, a process for treatinglead-toxic solid wastes in order to stabilize the leachable lead isdisclosed, comprising the steps of: (i) mixing the solid waste with asulfate compound, such as calcium sulfate dihydrate (gypsum powder) orsulfuric acid, having at least one sulfate ion for contacting wasteparticles and reacting with said leachable lead to produce asubstantially insoluble lead composition, such as anglesite and/orcalcium-substituted anglesite; and, (ii) mixing said solid waste andsulfate compound with a phosphate reagent, such as phosphoric acid,having at least one phosphate ion for reacting with said leachable leadto produce a substantially insoluble lead composition. The treatedmaterial from this process is substantially solid in form and passes thePaint Filter Test while satisfying the regulatory standard for TCLPlead. In all instances, application of this process has been found veryreliable in meeting the treatment objectives and in consistentlydecreasing waste volume.

It is an object of the present invention to provide a technology fortreatment of lead-containing solid waste and soil that produces anacceptably low level of leachable lead in the final product to complywith the statutory requirements of TCLP and to pass the Paint FilterTest.

Another object of the invention is to provide such a process whileproducing no wastewater or secondary waste streams during said process.

Still another object of the invention is to provide such a process whichalso causes the solid waste material to undergo a volume reduction as aresult of treatment.

Yet another object of the invention is to cause fixation of theleachable lead in the solid waste that is permanent under both ordinaryand extreme environmental conditions.

The invention relates to treatment methods employed to chemicallyconvert leachable metal in metal-bearing solid and liquid wastematerials to a non-leachable form by mixing the material with one or acombination of components, for example, lime or gypsum and phosphoricacid. The solid and liquid waste materials include contaminated sludges,slurries, soils, wastewaters, spent carbon, sand, wire chips, plasticfluff, cracked battery casings, bird and buck shots and tetraethyl leadcontaminated organic peat and muck. The metal-bearing materials referredto herein which the present invention treats include those materialshaving leachable lead, aluminum, arsenic (III), barium, bismuth,cadmium, chromium (III), copper, iron, nickel, selenium, silver andzinc. The present invention discloses a process comprising a single stepmixing of one or more treatment additives, and a process comprising atwo step mixing wherein the sequence of performing the steps may bereversible. The present invention provides a novel way of treating aplurality of metal-contaminated materials at a wide range of pH. Themethod works under acidic, alkaline and neutral conditions.

The processes of the present invention provide reactions that convertleachable metals, especially lead, into a non-leachable form which isgeochemically stable for indefinite periods and is expected to withstandacid rain impacts as well as the conditions of a landfill environment.

A first group of treatment chemicals for use in the processes of thepresent invention includes lime, gypsum, alum, halites, portland cement,and other similar products that can supply sulfates, halides, hydroxidesand/or silicates.

A second group consists of treatment chemicals which can supplyphosphate ions. This group includes products such as phosphoric acid,pyrophosphates, triple super phosphate (TSP), trisodium phosphate,potassium phosphates, ammonium phosphates and/or others capable ofsupplying phosphate anion when mixed with a metal-bearing processmaterial or with a metal-toxic hazardous waste. Depending on the processmaterial or waste (i) matrix (solid, liquid or mixture thereof), (ii)category (RCRA or Superfund/CERCLIS), (iii) chemical composition (TCLPlead, total lead level, pH) and (iv) size and form (wire fluff, shots,sand, peat, sludge, slurry, clay, gravel, soil, broken battery casings,carbon with lead dross, etc.) the metal-bearing material is mixed withone or more treatment chemicals in sufficient quantity so as to renderthe metal substantially non-leachable, that is, to levels below theregulatory threshold limit under the TCLP test criteria of the USEPA.For lead-bearing material, the treatment additives render the lead belowthe regulatory threshold limit of 5 mg/l by the TCLP test criteria ofthe USEPA. The disposal of lead-hazardous and other metal-hazardouswaste materials in landfills is precluded under land ban regulations.

It is an object of the present invention to provide a method of treatingmetal-bearing materials, contaminated soils and waste effluent, andsolid wastes containing hazardous levels of leachable metal. It is afurther object to provide a method which decreases the leaching of leadin lead-bearing materials to levels below the regulatory limit of 5 mg/lby TCLP test criteria.

It is another object of the present invention to provide a method toimmobilize lead to leachable levels below 5 mg/l by TCLP test criteria,through the use of inexpensive, readily accessible treatment chemicals.With this method the leachability of lead is diminished, usuallyallowing municipal landfill disposal which would not otherwise bepermitted.

Yet another object of the present invention is to provide a treatmentmethod for metal-bearing wastes, particularly lead-bearing wastes, whichcomprises a single step mixing process or a two-step process wherein thesequence of the two steps may be reversed.

Another object of the present invention is to provide a method oftreating a wide variety of lead bearing process materials, wire fluffand chips, cracked battery plastics, carbon with lead dross, foundrysand, lead base paint, leaded gasoline contaminated soils, peat andmuck, sludges and slurries, lagoon sediment, and bird and buck shots, inorder to render the material non-hazardous by RCRA definition, and passthe EPTOX, MEP, ANS Calvet and DI Water Extract tests.

Another object of the present invention is to extend the scope for broadapplication in-situ as well as ex-situ on small as well as largequantities of metal-bearing process materials or generated wastestreams.

The present invention provides a method which converts metal-toxicprocess materials and hazardous wastes into a material which has a lowerleachability of metal as determined by EPA's TCLP test. Such treatedwaste material can then be interned in a licensed landfill, a method ofdisposal only possible when the leachability of metal isdiminished/reduced to levels below the regulatory threshold limit byTCLP test criteria, e.g., lead below 5 mg/l.

The invention may be more fully understood with reference to theaccompanying drawings and the following description of the embodimentsshown in those drawings. The invention is not limited to the exemplaryembodiments but should be recognized as contemplating all modificationswithin the skill of an ordinary artisan.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 exhibits the single step mixing method of treatment chemicalsmetered into the pugmill or Maxon Mixer capable of processing leadhazardous waste materials at rates up to 100 tons/hour;

FIG. 2(a) exhibits the two step mixing method with addition of group onetreatment chemicals during step I and addition of group two treatmentchemicals during step II;

FIG. 2(b) exhibits the two step mixing method with addition of group twotreatment chemical(s) during step I and addition of group one treatmentchemical(s) during step II. The reversibility of steps and combinationof both steps into a single step is the discovery that is disclosed inthis invention and illustrated in FIGS. 1, 2(a) and (b); and

FIG. 3 illustrates schematically the process of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

According to the present invention, leachable lead in treated materialsis decreased to levels well below 5.0 mg/l, measured by TCLP testcriteria. Waste and process materials having a TCLP lead level in excessof 5 mg/l are considered hazardous and must be treated to be broughtinto compliance with regulatory-requirements. Other metal-bearingmaterials having leachable may also be treated according to the presentinvention to achieve acceptable metal levels.

The treatment technology according to another embodiment of the presentinvention consists of a two step process for treating contaminated soilsand/or solid waste materials with chemical treating agents that convertleachable lead to synthetic (man-made) substantially insoluble leadmineral crystals. As used here, "substantially insoluble" means theleachable lead content in the treated waste sample is less than 5.0 mg/lin the extract by the TCLP Test.

Treatment Chemicals and Additives

The treatment chemicals useful in the present invention may be dividedinto two groups. The addition of water with the additives may facilitatethe ultimate mixing and reaction.

A first group, "group one", comprises of a source of sulfate, hydroxide,chloride, fluoride and/or silicates. These sources are gypsum, lime,sodium silicate, cement, calcium fluoride, alum and/or like similarproducts.

The second group, "group two", comprises a source of phosphate anion.This group consists of products like phosphoric acid (phosphoric),pyrophosphates, triple super phosphate, trisodium phosphates, potassiumphosphates, ammonium, phosphates and/or similar compounds capable ofsupplying a phosphate anion.

The first step of this novel process comprises the reaction of leachablelead in contaminated soils or solid waste materials with a gypsumpowder, calcium sulfate dihydrate (CaSO₄.2H₂ O). Calcium sulfatedihydrate powder reacts with leachable and mobile lead species in wastesto form hard sulfates, which are relatively insoluble in water. In theinvention, the powder form of dry calcium sulfate dihydrate, or gypsum,is preferred for blending with lead contaminated materials because itprovides a uniform cover or dry coating over the surfaces of the wasteparticles and aggregates under low moisture conditions. The greatestbenefit and fastest reaction is achieved under conditions wherein 95% ofthe powder is passable through a 100 mesh sieve, and the remaining 5% ispassable through a 20 mesh sieve.

The amount of gypsum powder employed is typically from 0-30 percent ofthe weight of solid waste material being treated. The actual amountemployed will vary with the degree and type of lead contamination in thewaste material or soil, and with the initial composition as well as thecondition of the waste material, among other factors.

Alternatively, sulfuric acid, or alum in liquid or powder form can alsobe used as sources of sulfate ion in certain solid wastes that containsufficient calcium prior to treatment.

Treatment Method

At least one component from group one is added to the mixing vessel orreactor, preferably as a dry powder although slurries could be pumpedunder certain circumstances. At least one component from group two isadded to the mixing vessel or reactor as either liquid reagent or asgranular solid materials.

The ingredients of group one and group two can be added to the hazardouswaste materials simultaneously, and they are pre-mixed and added in asingle step. Alternatively, the components of group one and two can beadded sequentially in a two-step process with either component addedfirst. That is, the two steps may occur in any order. At least oneingredient of group one can be added in step I or step II. Likewise, atleast one ingredient of group two can be added in either step I or stepII. Enough water may be added to allow good mixing to prevent dustformation, and to permit good chemical reaction. Not too much water isadded to solid materials if the treated waste is to pass the paintfilter test.

In the first step of the instant process, a thorough and uniform mixingof gypsum powder with the solid waste is accomplished by mixing shreddedand screen waste particles with small gypsum particles in, for example,a grizzly or other mixing device. The calcium ions from the gypsumpowder displace lead from soil complexes and organic micelles present inthe contaminated soil and solid waste material The following equations(1) and (2) describe the reaction of leachable lead with gypsum.##STR1##

The reaction of lead with gypsum forms a "hard sulfate" whichcrystallizes into mineral species of the barite family --anglesites andcalcium-substituted anglesites--which are insoluble in water. Thesolubility product of lead sulfate is 1.8×10⁻⁸, indicating thatanglesite crystals would continue to develop over the geologic periods.

In the second step of the process, the solid waste material as amendedwith gypsum powder is treated with a phosphate-supplying reagent, suchas (for example), phosphoric acid. Upon contact with the soil or solidwaste, the phosphate-supplying reagent reacts chemically to immobilizethe remaining leachable lead. The phosphate-supplying reagent includesphosphate ion sources having one or more reactive phosphate ions, suchas phosphoric acid, trisodium phosphate, a potassium phosphate andmonobasic or dibasic calcium phosphates.

The quantity of phosphate-supplying reagent employed will vary with thecharacteristics of the solid waste being treated, including particularlysuch factors as leachable lead content, total lead, and bufferingcapacity, among other factors. It has been determined that in mostinstances a quantity of phosphoric acid up to 30 percent of the weightof the waste material is sufficient. The concentration of phosphoricacid in solution will typically range from about 2-75 percent by weight.The solution and treatment process are maintained above 30° F. to permitthe handling of the phosphoric acid as a liquid reagent. Below 30° F.,the phosphoric acid tends to gel while water freezes to form ice, thuscreating material handling problems.

Free lead, along with calcium ions found in the solid waste (includingthose imparted through the first step of the process), reacts with thephosphate to form insoluble superhard rock phosphates or calciumsubstituted hydroxy lead apatites as shown in equation (3a and b):##STR2##

The phosphate ions are added to the contaminated soils in solution form;for example, phosphoric acid may be added to water in amounts rangingfrom about 2 percent to about 75 percent by weight. Phosphoric aciddecomposes carbonates and bicarbonates in wastes leading to thesynthesis of apatites and evolution of carbon dioxide gas. Destructionof carbonates and bicarbonates contributes to desirable volumereductions.

Although water molecules are generated during the carbonate andbicarbonate decomposition process, it is preferred to have soil moistureat about 10 per cent to about 40 per cent by weight of the soil in orderto accelerate the fixation of the leachable lead with the phosphateions. At this moisture range, material handling is also easy andefficient. It is apparent from Equations (2), (3a) and (3b) that gypsumand phosphoric acid decompose carbonates and bicarbonates duringsynthesis of new stable minerals of the barite, apatite, andpyromorphite families in soils (as shown in Table I). Decomposition ofcarbonates and bicarbonates is usually associated with the evolution ofcarbon dioxide, formation of hydroxyl group, (OH--), and the release ofwater molecules. As the water evaporates and carbon dioxide moleculesare lost to the atmosphere, the treated waste mass and volume aredecreased significantly.

The solid sulfate powder and the phosphate-supplying reagent are addedto contaminated soil and solid waste material having a typical moisturecontent ranging from about 10 percent to about 40 percent by weight. Ata moisture level within the foregoing range, the curing time of thetreated materials is approximately 4 hours, which provides adequate timefor chemical reactions to occur and immobilize the leachable leadspecies. Crystals of various lead mineral species begin to formimmediately, but will continue over long time periods with an excess oftreatment chemicals present. This contributes to "self-healing," asnoted during treatability studies as well as full scale treatmentoperations.

Under the foregoing conditions, the immobilization of leachable leadoccurs in a relatively dry environment because no wet byproducts,slurries or wastewater are produced by the process of the presentinvention. Operation of the process under relatively dry conditionsbeneficially allows cost-efficient handling of the contaminated soilsand the waste materials. This allows compliance with Paint Filter Testfor solid wastes required by USEPA and RCRA approved solid wastelandfill facilities. Effective mechanical mixing, as by a pug mill orother such mixing device, eliminates the need for diffusion in thenonaqueous solid waste matrix.

The water resistant and insoluble lead minerals synthesized in soils andsolid wastes according to this process are stable, and would behave likenaturally occurring rock phosphates and hard sulfates. A list of thesesynthetic lead mineral species and complexes is presented in Table Ibelow, in order of the relative abundance found during characterizationof treated soil by x-ray florescence spectrometry, polarized lightmicroscopy (PLM) and scanning electron microscopy (SEM).

                  TABLE I                                                         ______________________________________                                        Synthetic Mineral Species of Lead Detected in a Treated Sample                (Listed in Decreasing Order of Abundance)                                     ______________________________________                                        31-41%      Calcium Substituted Hydroxy Lead Apatites,                                    Ca.sub.0.5-1.5 Pb.sub.3.5-4.5 (OH)(PO.sub.4).sub.3                28-29%      Mixed Calcium Lead Phosphate Sulfates,                                        Ca.sub.0.05-0.2 Pb.sub.0.8-0.95 (PO.sub.4).sub.0.15-0.5                       (SO.sub.4).sub.0.25-0.75                                          22-22%      Mixed Calcium Anglesites,                                                     Ca.sub.0.05-0.3 Pb.sub.0.7-0.95 SO.sub.4)                         3-6%        Anglesites, PbSO.sub.4                                            2-7%        Lead Hydroxy/Chlor Apatite, Pb.sub.5 (PO.sub.4).sub.3                         (OH).sub.0.5 Cl.sub.0.5                                           1-3%        Pyromorphite, Pb.sub.3 (PO.sub.4).sub.2                           1-2%        Organo-Lead Phosphate Sulfate,                                                Humus-o-Pb.sub.3 (PO.sub.4)(SO.sub.4)                             ______________________________________                                    

Some of the chemical reactions that occur during the curing stage, andlead to the development of mixed minerals containing both sulfates andphosphates, are illustrated in equations (4) and (5). ##STR3##

The process of the present invention beneficially decreases the volumeof the waste materials through: (i) the evolution of carbon dioxideduring the chemical decomposition of carbonates and bicarbonates, uponreaction with the acidic components in gypsum and phosphoric acid, and(ii) hardening and chemical compaction as a result of the synthesis ofnew minerals which result in changes in interstitial spaces andinterlattice structures. Applications of the process on a leadcontaminated soil was associated with pore space decrease from 38.8% to34.3% by volume. A decrease in pore space was associated with increasedcompaction of the treated soils and a decrease in overall waste volumeranging from 21.4% to 23.0%. For different waste types, the volumedecrease varies with the amount of treatment chemicals used in theprocess. In another lead toxic solid waste, application of this processresulted in a volume decrease of the order of 36.4% while decreasing theleachable lead to levels below the regulatory threshold.

This reduction in volume of the contaminated soil and the solid wastematerial makes the process of the present invention particularlybeneficial for off-site disposal in a secured landfill by cutting downthe costs of transportation and storage space. The process can beaccomplished at a cost-efficient engineering scale on-site or off-sitefor ex-situ treatment of lead-toxic solid wastes. This innovativetreatment technology also offers a great potential for in-situapplication to immobilize lead most economically without generation ofany wastewater or byproducts.

FIG. 3 illustrates schematically the process of the present invention.The lead-contaminated uncontrolled hazardous waste site 10 withlead-toxic wastes is subject to excavation and segregation 20 of wastepiles based on their total lead and TCLP lead contents into (a) heavilycontaminated pile 30A, (b) moderately contaminated waste pile 30B and(c) least contaminated waste pile 30C. The staged soil and solid wastematerial in piles 30A, 30B and 30C is subjected to grinding, shredding,mixing 40 and screening 50 through an appropriately sized mesh sieve.The screening yields particles that are usually less than 5 finches indiameter for mixing with gypsum powder 60 in a grizzly that allows auniform coating of gypsum over the soil particles and waste aggregatesduring the grinding, shredding and/or mixing step. Alternatively, asshown by the dashed line, gypsum powder 10 may be added continuously tothe screened solid waste material in prescribed amounts as determinedduring treatability trials. Most of the leachable lead binds chemicallywith gypsum at molecular level to form lead sulfate, which crystallizesinto a synthetic nucleus of mixed calcium anglesite and pure anglesiteminerals identified in the treated material by chemical microscopytechniques.

The gypsum-coated waste particles and aggregates are then transported ona belt conveyor 70 or other conveying means to an area where aneffective amount of phosphoric acid solution 80 of specified strengthsin water 90 is added or sprayed just prior to thorough mixing in a pugmill 100 (or other mixing means). The temperature of the phosphoricsolution is preferably maintained above 30° F. to prevent it fromgelling. The treated soil and wastes are subject to curing 110 anddrying 120 on a curing/drying pad, or may less preferably be cured anddried using thermal or mechanical techniques. The end product of theprocess passes the Paint Filter Test. During the curing time of aboutfour hours, various "super-hard phosphate" mineral species, such ascalcium-substituted hydroxy lead-apatites and mixed calcium-leadphosphate-sulfate mineral species, are formed in treated waste media130. Crystals of these mineral species (in early stages of development)have been identified in the treated soil materials and solid wastes bygeo-chemical and microscopy techniques like PLM and SEM.

The proportions of waste materials and reagents used in the process maybe varied within relatively wide limits. For example, the amount ofgypsum powder should be sufficient to produce lead sulfate incontaminated solid or solid waste material. In addition, the amount ofphosphate-supplying reagent is prescribed in an amount sufficient toproduce mineral species such as hydroxy-lead apatite in contaminatedsoil or solid waste material during a relatively short curing time of 4hours, usually ranging from about 3 to about 5 hours. Further drying ofthe treated material may take 24 to 96 hours, but has not been requiredin any application to date. Table II documents the optimum curing timeof 4 hours for the process. In all instances, the leachable lead asmeasured by the EP Toxicity Test Procedure was found below 0.6 mg/l andthe differences between analytical values below this level andstatistically insignificant.

                  TABLE II                                                        ______________________________________                                        Documentation of Optimum Curing Time                                          Using EP Toxicity Test criteria for lead fixation                                                  EP Toxic Pb Concentration                                          EP Toxic Pb                                                                              in mg/l found in processed                               Waste     (Untreated sample at a Curing Time of                               Matrix    Sample)    4 Hrs.    48 Hrs.                                                                             96 Hrs.                                  Category  mg/l       mg/l      mg/l  mg/l                                     ______________________________________                                        Pb Toxic  495        0.4       0.4   0.6                                      Soil A                                                                        Pb Toxic  46         0.3       0.2   0.2                                      Soil B                                                                        Pb Toxic  520        0.3       0.5   0.5                                      Soil C                                                                        ______________________________________                                    

The amount of the gypsum powder and the phosphoric acid employed will bedependent on the amount of contaminant present in the soil, initialcharacteristics of the solid waste material, whether the material isin-situ or is excavated and brought to an off-site facility fortreatment; the same is true for other sulfate compounds and phosphatereagents. The following Example I describes various ratios of thechemical reagents for application to the excavated lead-contaminatedsolid wastes in order to render the leachable lead substantiallyinsoluble; i.e., to reduce the leachable lead to levels below 5.0 mg/lby EP Toxicity Test lead and TCLP Test criteria now in force undercurrent land-ban regulations.

Temperature and Pressure

Ambient temperature and pressure may be used for the disclosed treatmentprocess, permitted the operations of the feeding and mixing equipmentallow such. Under sub-freezing conditions, phosphoric acid may be heatedto 50° F. to prevent it from gelling and in order to keep it in apumpable viscosity range.

Treatment System Design

The treatment may be performed under a batch or continuous system ofusing, for example, a weight-feed belt or platform scale for themetal-hazardous waste materials and a proportionate weight-belt feedsystem for the dry ingredient or ingredients and powders of at least oneof the groups. A metering device, e.g., pump or auger feed system, mayinstead, or additionally, be used to feed the ingredients of at leastone of the groups.

EXAMPLE 1 Single Step Mixing of Treatment Chemicals

A lead contaminated soil from a battery cracking, burning, and recyclingabandoned site was obtained and treated with group one and group twochemicals in one single step at bench-scale. The contaminated soilcontained total lead in the range of 11.44% to 25.6% and TCLP lead inthe range of 1781.3 mg/l to 3440 mg/l. The bulk density of contaminatedsoil was nearly 1.7 g/ml at moisture content of 10.3%. The contaminatedsoil pH was 5.1 with an oxidation reduction potential value of 89.8 mV.To each 100 g lot of lead hazardous waste soil, sufficient amounts ofgroup one and group two treatment chemicals and reagents were added asillustrated in Table III, in order to render it non-hazardous by RCRA(Resource Conservation and Recovery Act) definition.

                  TABLE III                                                       ______________________________________                                                                        TCLP                                                                          Lead                                          Test Run                                                                             Treatment Additive(s)    (mg/l)                                        ______________________________________                                        I      5% lime, 5% gypsum, 10.2% phosphoric                                                                   0.5                                           II     12% phosphoric, 10% potassium sulfate                                                                  2.2                                           III    12% phosphoric, 10% sodium sulfate                                                                     3.5                                           IV     15% TSP                  3.7                                           V      12% phosphoric, 10% Portland Cement I                                                                  0.2                                           VI     12% phosphoric, 10% Portland Cement II                                                                 0.9                                           VII    12% phosphoric, 10% Portland Cement III                                                                0.3                                           VIII   12% phosphoric, 10% gypsum                                                                             4.6                                           IX     15% TSP, 10% Portland Cement I                                                                         0.1                                           X      15% TSP, 10% Portland Cement II                                                                        0.2                                           XI     15% TSP, 10% Portland Cement III                                                                       0.2                                           XII    15.1% phosphoric         3.6                                           XIII   10% trisodium phosphate, 10% TSP                                                                       1.2                                           XIV    6.8% phosphoric, 4% TSP  4.5                                           XV     10% gypsum               340                                           XVI    12% phosphoric, 5% lime  0.9                                           Control                                                                              Untreated Check          3236.0                                        ______________________________________                                    

It is obvious from TCLP lead analyses of fifteen test runs that thesingle step mixing of at least one component of either or both group oneand group two treatment chemicals is very effective in diminishing theTCLP lead values. In test run I, mixing of lime and gypsum from groupone additives and phosphoric from group two decreased the TCLP lead tolevels below 1 mg/l from 3440 mg/l with a curing time of less than 5hours. Although the treatment chemicals of group two are more effectivein decreasing the TCLP lead than the treatment chemicals of group one,as illustrated by the comparison of test runs XII and XV for this wastesoil, but the combined effect of both groups is even more pronounced indecreasing the leachable lead. Results of these bench-scale studies wereconfirmed during engineering-scale tests. Single step mixing of 5% lime,11.76% phosphoric acid and 15% water in a 2000 g hazardous soildiminished the TCLP lead values from 3440 mg/l to 0.77 mg/l in less than5 hours. Likewise, single step mixing of 300 g Triple Super Phosphate(TSP), 200 g Portland Cement (PC) and 300 ml water in 200 g hazardoussoil decreased the TCLP lead to levels below 0.3 mg/l within arelatively short curing time. Single step mixing of both groups oftreatment chemicals can dramatically reduce treatment costs making thisinvention highly attractive and efficient for commercial use.

The first advantage of using lime and phosphoric acid combination overthe use of TSP and PC is that in the former a volume decrease of 6% wasrealized when compared to the original volume of untreated material. Inthe later case, a volume increase of 37% was measured due to hydrationof cement. The second advantage of using phosphoric and lime combinationis that the mass increase is less than the mass increase when TSP and PCare added. Quantitatively, the mass increase in this hazardous wastesoil treatment was approximately 16.7% due to combination of lime andphosphoric whereas the mass increase was about 40% due addition of ITSPand PC. And therefore, those skilled scientists and engineers learningthis art from this patent, must make an economic judgement for each leadcontaminated process material and waste stream which chemical quantityfrom each group would be most effective in rendering the treatedmaterial non-hazardous.

The third advantage in using lime and phosphoric over the use of TSP andPC is that the former does not change in physical and mechanicalproperties of original material and if a batch fails for shortage oftreatment chemicals, it can be retreated rather easily by adding more ofthe treatment reagent. The material treated with PC hardens and may forma monolith which is difficult to retreat in case of a batch failure.

EXAMPLE 2 Interchangeability of Two Step Mixing Method

In the lead contaminated soil from the abandoned battery recyclingoperations, the treatment chemicals of either group can be added firstand mixed thoroughly in an amount sufficient to decrease the TCLP leadbelow the regulatory threshold. Two step mixing method of the group oneand group two treatment additives is as effective as single step mixingof same quantity of treatment chemicals selected from group one andgroup two.

Table IV illustrates data that confirm that the application of group onetreatment chemicals in step I is about as effective as application instep II. The same is true for group two treatment chemicals. Thus, thetwo steps are essentially interchangeable. The reversibility of thesteps according to the present invention make it very flexible foroptimization during commercial use, scaling up and retreatment of anybatches that fail to pass the regulatory threshold criteria.

                  TABLE IV                                                        ______________________________________                                        Treatment Additives                                                           ______________________________________                                        Two Step Mixing Methods                                                                                        Total TCLP                                   Test                             Lead  Lead                                   Run   Step I       Step II       %     mg/l                                   ______________________________________                                        I     10% gypsum & 12% phosphoric                                                                              20.8  1.8                                          2% lime      acid (Group II)                                                  (Group I)                                                               II    12% phosphoric                                                                             10% gypsum &  24.4  1.9                                          (Group II)   2% lime                                                                       (Group I)                                                  III   10% gypsum   10.6% phosphoric                                                                            24.4  3.4                                          (Group I)    (Group II)                                                 IV    10.6% phosphoric                                                                           10% gypsum    22.4  3.5                                          (Group II)   (Group I)                                                  ______________________________________                                        Single Step Mixing Method                                                     ______________________________________                                        V      10% gypsum and 12% phosphoric                                                                       23.6    3.5                                      Un-    Control/Check         23.1    3440                                     treated                                                                       ______________________________________                                    

EXAMPLE 3 Retreatability and Single Step Mixing

A sample of hazardous cracked battery casings of 1/2"-1" size containing14% to 25.2% total lead and about 3298 mg/l of TCLP was obtained forseveral test runs of the invention to verify the retreatability ofbatches that fail because of the insufficient dose of treatment chemicaladded. The results of initial treatment and retreatment are presented inTable IV and compared with single step mixing treatment additives fromboth groups. About 200 g of hazardous material was treated with 10.5%phosphoric acid, 2.5% gypsum and 1.25% lime, all mixed in one singlestep. The TCLP lead was decreased from 3298 mg/l to 2.5 mg/l as a resultof single step mixing in test run V (TABLE V).

When the amount of additive from group two was less than the optimumdose needed, the TCLP lead decreased from 3298 mg/l to (i) 1717 mg/lwhen 4.2% phosphoric and 1% lime were added during step I and IIrespectively and (ii) 2763 mg/l when 4.2% phosphoric and 5% gypsum wereadded, compared to untreated control.

Since the TCLP lead did not pass the regulatory criteria of 5 mg/l,treated material from test run I and II was retreated during test runIII and IV, respectively, using sufficient amounts of phosphoric acid(an additive from group two) in sufficient amount to lower the TCLP leadto 2.4 mg/l and 2.5 mg/l, respectively. Furthermore, this exampleconfirms that lime is more effective in decreasing TCLP lead than gypsumamong different additives of group one. And as a result, the requirementof group two treatment reagent is lessened by use of lime over gypsum.The example also illustrates that one or more compounds of the samegroup can be used together to meet the regulatory threshold limit.

                  TABLE III                                                       ______________________________________                                        Treatment Additives                                                           ______________________________________                                        Two Step Mixing Methods                                                                                            TCLP                                                                          Lead                                     Test Run                                                                              Step I          Step II      mg/l                                     ______________________________________                                        I       4.2 phosphoric  1% lime      1717                                     II      4.2% phosphoric 5% gypsum    2763                                     Untreated                            3296                                     Control                                                                       ______________________________________                                        Retreatment (Single Step Mixing) Method                                       ______________________________________                                        III-I   6.8% phosphoric          2.4                                          IV-II   8.5% phosphoric          3.5                                          ______________________________________                                        Single Step Mixing                                                            ______________________________________                                        V       10.5% phosphoric, 2.5% gypsum, 1.25% lime                                                              2.5                                          ______________________________________                                    

EXAMPLE 4 Wide Range of Applications and Process Flexibility in CuringTime, Moisture Content and Treatment Operations

TABLE IV illustrates different types of waste matrix that have beensuccessfully treated employing the one step and two step mixingtreatment additives from group one and group two. For these diversewaste types and process materials, total lead ranged from 0.3% to 23.5%.This example discloses the flexibility and dynamics of the treatmentprocess of the invention in rendering nonhazardous, by RCRA definition,a wide range of lead-hazardous and other metal-hazardous materialswithin a relatively short period of time, usually in less than 5 hours.It is expected that this process will also render bismuth, cadmium,zinc, chromium (III), arsenic (III), aluminum, copper, iron, nickel,selenium, silver and other metals also less leachable in these differenttypes of wastes. The moisture content of the waste matrix is notcritical and the invented process works on different process materialsand waste types independent of the moisture content. The treatmentoperations can be carried out at any level--bench, engineering, pilotand full-scale, on relatively small amounts of hazardous waste materialin laboratory to large amounts of contaminated process materials, soils,solid wastes, waste waters, sludges, slurries and sediments outdooron-site. The process is applicable in-situ as well as ex-situ.

Although the present invention has been described in connection withpreferred embodiments, it will be appreciated by those skilled in theart that additions, modifications, substitutions and deletions notspecifically described may be made without departing from the spirit andscope of the invention defined in the appended claims.

                                      TABLE VI                                    __________________________________________________________________________    UNIVERSE OF APPLICATION FOR THE INVENTION MAECTITE TREATMENT PROCESS                                             LEACHABE LEAD                                                                 (MG/L)                                     LEAD CONTAMINATED TREATMENT  TOTAL Before                                                                              After VOLUME                         WASTE TYPE        ADDITIVE   LEAD %                                                                              Treatment                                                                           Treatment                                                                           DECREASE                       __________________________________________________________________________                                                   %                              OLD DIRT          3.4%                                                                              Phosphoric*                                                                          2.2   164.4 1.5   16.7                           WASTE WITH BROKEN 8.1%                                                                              Lime   2.7   197.5 ND (<.5)                             BATTERY CASING    1%  Gypsum and                                                                3.4%                                                                              Phosphoric                                              SLAG-LEAD SMELTER 10.2%                                                                             Phosphoric                                                                           6.6   21.3  2.0                                  LEAD-BIRD SHOT    16% Phosphoric                                                                           16.1  3720  ND (<.5)                                               14% Lime and                                                                  30% Gypsum                                                  LEAD-BUCK SHOT    16% Phosphoric                                                                           11.4  1705  ND (<.5)                                               14% Lime and                                                                  28% Gypsum                                                  BATTERY CASINGS   5%  Gypsum 12    288   0.6   0                              ORGANIC HUMUS SOIL                                                                              0.5%                                                                              Lime   1.9   23.2  ND (<.5)                                                                            29                                               2.0%                                                                              Phosphoric                                              50:50 MIXTURE OF  4%  Gypsum .5    687   0.7   3.3                            CASINGS AND SAND  4%  Phosphoric   422.2 0.95  23.6                           SOLID WASTE SOIL  3%  Lime   23.5  12.0  6.0                                  Contaminated With 12% Phosphoric                                              Tetrethyl lead                                                                SOIL CONTAMINATED 10% Gypsum 4.74  590   3.7                                  WITH LEADED GASOLINE                                                                            6%  Phosphoric                                                                3%  Lime   3.2   213   1.6                                                    5.1%                                                                              Phosphoric                                              CARBON WITH LEAD DROSS                                                                          4.7%                                                                              Phosphoric                                                                           12.6  105.6 0.5                                  WIRE FLUFF        1.7%                                                                              Phosphoric                                                                           0.3   19    0.7                                  WIRE CHIP         0.75%                                                                             Phosphoric                                                                           0.4   28    ND (<.2)                             LAGOON SEDIMENT   0.6%                                                                              TSP    0.3   3.9   0.23                                                   0.5%                                                                              Phosphoric   5.6   0.3                                  SLUDGE-INDUSTRIAL WASTE      2.2   59.3  1.6                                  RCRA ORGANIC SLUDGE                                                                             0.6%                                                                              Phosphoric                                                                           9.4   580   ND (<.5)                                               10% Gypsum                                                  FILTER CAKE       8.5%                                                                              Phosphoric                                                                           2.9   245.3 1.1                                  GRAVEL            5%  Gypsum 0.16  7.5   0.5                                                    2.2%                                                                              Phosphoric                                              ROAD GRAVEL       10% Gypsum 0.34  46    ND (<.5)                                               8.4%                                                                              Phosphoric                                              MIXTURE OF BATTERY                                                                              2.5%                                                                              Gypsum                                                  CASINGS (SOLID WASTE)                                                                           3.4%                                                                              Phosphoric                                                                           1.3   75    0.6   19.6                           AND SOIL                                                                      INDUSTRIAL WASTE  1 g Lime   2.75  91    0.7                                  (B)               3.4%                                                                              Phosphoric                                              INDUSTRIAL PROCESS                                                                              3.4%                                                                              Phosphoric                                                                           1.3   61    ND (<.5)                             MAT. (G)                                                                      SOIL (B)          3.4%                                                                              Phosphoric                                                                           4.1   129.5 0.6   25.6                           SOIL (S)          50% Gypsum 11    <0.01                                      SOIL (O)          1.3%                                                                              Phosphoric                                                                           0.38  34.6  ND (<.5)                             SOIL (C)          5%  Lime   11.78 130.6 0.33                                                   8.5%                                                                              Phosphoric                                              BATTERY CASINGS   5%  Gypsum 2.5   110.1 1.9                                                    3.4%                                                                              Phosphoric                                              GRAY CLAY SOIL    5%  Trisodium                                                                            2.2   46.6  0.2                                                        Phosphate                                               __________________________________________________________________________

EXAMPLE 5

Nearly twenty (20) different chemicals and products from various vendorsand supply houses were screened for chemical fixation of leachable leadin hazardous solid waste samples. Only six (6) of these treatmentschemicals were found effective in decreasing the leachable lead asmeasured by: (1) the EP Toxicity Test and (2) the TCLP Test. Table VIIpresents a summary of leachable lead found in untreated and treatedwaste samples allowed to cure for a minimum of 4 hours after treatmentwith at least one of the effective chemicals. Treatment chemicals foundrelatively ineffective for lead fixation included a variety ofproprietary products from American Colloid Company and Oil Dri,different sesquioxides like alumina and silica, calcium silicate, sodiumsilicate, Portland cement, lime, and alum from different vendors.Results for these ineffective chemicals are not shown in Table VII.

                  TABLE VII                                                       ______________________________________                                        Relative effectiveness of various treatment chemicals                         screened to decharacterize the lead-toxic solid wastes                                            Leachable Lead                                                                in mg/l                                                                         Toxicity EP TCLP                                        Treatment Chemical (Step)                                                                           Test     Test                                           ______________________________________                                        I.   Untreated Control    221.4    704.5                                      II.  Single Treatment Chemical                                                     (One Step Treatment)                                                     a.   Sulfuric Acid (I)    11.7     39.8                                       b.   Phosphoric Acid (I)  1.0      5.9                                        c.   Superphosphate Granular (I)                                                                        2.7      11.4                                       d.   Liquid Phosphate Fertilizer (I)                                                                    19.4     64.3                                       e.   Gypsum Powder (I)    24.9     81.8                                       f.   Sodium Phosphate (I) 28.7     93.9                                       III. Two Step Treatment                                                       g.   Sulfuric (I) & Lime (II)                                                                           20.6     68.1                                       h.   Gypsum Powder (I) & Alum (II)                                                                      3.9      15.3                                       i.   Sodium Phosphate (I) &                                                                             3.1      12.6                                            Phosphoric (II)                                                          j.   Gypsum (I) & Phosphoric (II)                                                                       N.D.*    1.6                                        IV.  Three Step Treatment                                                     k.   Gypsum (I), Alum (II) &                                                                            12.8     43.3                                            Sodium Phosphate (III)                                                   l.   Gypsum (I), Phosphoric (II) &                                                                      N.D.*    1.4                                             Sodium Phosphate (III)                                                   ______________________________________                                         *N.D. means nondetectable at <0.50 mg/l.                                 

Evaluation of a single treatment chemical in one step reveals thatphosphoric acid was most effective in fixation of leachable leadfollowed by granular super-phosphate, a fertilizer grade productavailable in nurseries and farm supply houses. However, neithertreatment effectively treated leachable lead to the USEPA treatmentstandard of 5.0 mg/l by TCLP methodology.

Although both phosphoric acid and granular superphosphate were effectivein meeting the now obsolete EP Toxicity Test criteria at 5.0 mg/l, thistest has been replaced by TCLP Test criteria for lead of 5.0 mg/l.Single application of the phosphoric acid, granular superphosphate orany other chemical was short of meeting the regulatory threshold of 5.0mg/l by TCLP Test criteria for lead.

In a two-step treatment process, application of gypsum during Step I andtreatment with phosphoric acid in Step II resulted in decrease ofTCLP-lead consistently and repeatedly below the regulatory threshold of5.0 mg/l. The results of this two-step treatment process utilizinggypsum in Step I and phosphoric acid in Step II are most reliable andhence, the two-step process may be applied to a wide variety of leadcontaminated wastes as exhibited in Example II.

A three-step process, as set forth in Table VII, was not perceived to beas economically viable as a two-step treatment process, despite itsability to reduce lead levels in satisfaction of the TCLP Test criteria.A process that employees the beneficial combination of treatment firstwith a sulfate compound and then with a phosphate reagent in accord withthe present invention, in combination with one or more additionaltreatment steps, may nevertheless be within the scope of the invention.

In order to illustrate the relative proportions of two chemicals, e.g.,gypsum and phosphoric acid, needed for treatment of lead-toxic wastes,three soil samples from a lead contaminated test site were processedusing the present invention, in which gypsum powder was used in thefirst step, and phosphoric acid solution in water at concentrations ofabout 7, 15 and 22 percent by weight in the second step. The soil wasmeasured for lead content in accordance with the EP Toxicity Test beforeand after treatment. A level of leachable lead below 5 mg/l wasconsidered non-hazardous according to this procedure. During these testruns, the EP Toxicity Test criteria were in force for treated wastematerial. The results of these tests are set forth in Table VIII:

                  TABLE VIII                                                      ______________________________________                                        Effectiveness in Fixation and Stabilization of                                Leachable Lead in Lead Toxic Soils                                                                 EP TOXIC LEAD                                                                 TEST RESULTS                                                      PROCESS STEPS Before   After                                         Soil Sample                                                                              Gypsum    Phosphoric                                                                              Treat- Treat-                                  (Lead-toxic                                                                              Step I    Step II   ment   ment                                    waste)     (g/kg soil)                                                                             (g/kg soil)                                                                             mg/l   mg/l                                    ______________________________________                                        1.  Low lead   20        10      8      <0.1                                      contamination                                                             2.  Moderate   30        20      61     <0.1                                      contamination                                                             3.  High lead  40        30      3,659  1.7                                       contamination                                                             ______________________________________                                    

The foregoing results demonstrate that the process of the presentinvention was effective in all three samples, representing 3 differentlevels of lead contamination. The process is flexible and is usuallyoptimized during bench scale treatability studies for each waste type toimmobilize the leachable lead and to decharacterize or transform thelead-toxic waste into non-toxic solid waste acceptable to TSD facilitiesunder current land ban regulations. A net reduction of 36.4% in wastevolume through use of the instant process has been observed. Typicalvolume reductions are set forth in Table IX.

                  TABLE IX                                                        ______________________________________                                        Changes in Solid Waste Volume                                                 as a Result of Treatment with the Two-Step Process                                      SOLID WASTE VOLUME                                                              Initial    Final (After                                           SOLID WASTE (Before    Application                                                                              Decrease in                                 MATERIAL    Application                                                                              of Process Waste                                       (Treatment Scale)                                                                         of Process)                                                                              and Curing)                                                                              Volume (%)                                  ______________________________________                                        1.  Low toxic soil                                                                            3850   cu. yd.                                                                             2450 cu. yd.                                                                             36.4                                      (full scale)                                                              2.  Lead-toxic                                                                    Solid waste                                                                   (Bench Scale)                                                                 Test Run I  106.1  cu. in.                                                                             81.51                                                                              cu. in.                                                                             23.0                                      Test Run II 22.0   cu. in.                                                                             17.3 cu. in.                                                                             21.4                                  ______________________________________                                    

The most profound effect of the process of the present invention is at astructural level, where the break-down of granular aggregates isassociated with a loss of fluffiness and a decrease in pore space andincreased compaction due to physical, mechanical and chemical forces atdifferent levels. At a molecular level, phosphoric acid breaks down theminerals containing carbonates and bicarbonates, including cerussites,in stoichiometric proportions. Soon after the addition of phosphoricacid to a solid waste containing cerussites, extensive effervescence andfrothing becomes evident for several minutes and sometimes for a fewhours. The phosphoric acid breaks down the acid sensitive carbonates andbicarbonates leading to the formation of carbon dioxide, water andhighly stable and insoluble sulfate and phosphate mineral compounds.Thus, structural changes due to interlattice reorganization as well asinterstitial rearrangement in waste during processing are associatedwith an overall decrease in waste volume. Depending on the extent ofcarbon dioxide loss from the breakdown of carbonates and bicarbonatespresent in the lead-toxic solid waste, the process may lead to a slightloss of waste mass as well. Water generated during the chemicalreactions is lost by evaporation, which further decreases the mass andvolume of the treated solid wastes and soils.

The cost of the process of the present invention is moderate to low,depending upon (i) waste characteristics, (ii) treatment system sizing,(iii) site access, (iv) internment of final disposition of treatedmaterial and (v) site support requirements. The costs of treatment anddisposal are presently on the order of $115 per ton of lead-toxic waste,as compared to off-site conventional treatment and disposal costs ofover $250 per ton if no treatment in accord with the invention had beenperformed. Moreover, recent land ban regulations would prohibit thedisposal of all lead-toxic wastes in landfills. The foregoing Examplemakes clear that the process of the present invention provides anefficient technology that is economically attractive and commerciallyviable in meeting regulatory criteria for landfills.

EXAMPLE 6

The process of the present invention was applied on bench scale to fivedifferent lead-toxic waste materials that were characterized for totallead, TCLP-lead, moisture content and pH before and after treatment. Acuring time of 5 hours was allowed for completion of the treatmentprocess. The results compiled in Table X exhibit the profound effects ofthe process in decreasing the TCLP lead in a wide range of lead-toxicsoils and solid wastes containing total lead as high as 39,680 mg/kg andTCLP lead as high as 542 mg/l. In each of the five cases, the instantprocess immobilizes the leachable lead to levels below the regulatorythreshold of 5 mg/l set by the TCLP Test criteria for lead currently inforce under the land ban regulations of the United States EnvironmentalProtection Agency.

                  TABLE X                                                         ______________________________________                                        Typical changes in solid waste characteristics                                due to process effects                                                                       MEASURED VALUES                                                SOLID WASTE      Before    After Treatment                                    CHARACTERISTICS  Treatment & Curing                                           ______________________________________                                        I.     Lead-toxic SW-A                                                               Total lead, % 1.442     1.314                                                 TCLP-Lead, mg/l                                                                             542.0     2.0                                                   Moisture, %   23.0      33.0                                                  pH, S.U.      8.1       4.8                                            II.    Lead-toxic SW-B                                                               Total lead, % 0.847     0.838                                                 TLCP-Lead, mg/l                                                                             192.0     2.4                                                   Moisture, %   27        36                                                    pH, S.U.      8.0       5.3                                            III.   Lead-toxic SW-C                                                               Total lead, % 3.968     3.066                                                 TLCP-Lead, mg/l                                                                             257.6     1.0                                                   Moisture, %   10.0      18.1                                                  pH, S.U.      7.2       4.5                                            IV.    Lead-toxic SW-D                                                               Total lead, % 2.862     2.862                                                 TLCP-Lead, mg/l                                                                             245.3     0.38                                                  Moisture, %   71.6      84.1                                                  pH, S.U.      8.1       6.3                                            V.     Lead-toxic SW-E                                                               Total lead, % 0.16      0.12                                                  TLCP-Lead, mg/l                                                                             7.5       1.87                                                  Moisture, %   12.3      23.0                                                  pH, S.U.      7.0       5.4                                            ______________________________________                                    

It is obvious from Table X that the instant process operates over a widerange of moisture and pH conditions. It is associated with 8 to 11% risein moisture content. The end product of the treatment process maycontain moisture in a typical range of 18% to 36% on a dry weight basis.The end product passes the Paint Filter Test for solids and there arenot other byproducts or side streams generated during the process. Thetreated solid waste is cured in 4 to 5 hours and may be allowed to dryfor 2 to 3 days after treatment for loss of unwanted moisture prior tofinal internment and disposition. This time is sufficient for the TCLPTests to be completed as part of the disposal analysis under land banregulations enforced by the USEPA.

It is necessary to establish the quantities of gypsum and phosphatereagent on a case-by-case basis, because the consumption of thesematerials will depend not only upon the initial lead level in the wasteor soil, but also upon other waste characteristics such as cationexchange capacity, total buffering capacity, and the amounts ofcarbonates and bicarbonates present, among others. Bench scaletreatability studies for each solid waste considered will be necessaryto determine the optimum levels of the materials that are employed. Thetreatability studies are designed to optimize the amount and grade ofgypsum powder (or other sulfate compound) needed during step I, and theamount and concentration of phosphoric acid (or other phosphatecompound) needed in step II for cost-effective operation of thetreatment system. Those skilled in the art are knowledgeable of suchbench studies, which are usually carried out as precursors to full scaletreatment.

Although the present invention has been described in connection withpreferred embodiments, it will be appreciated by those skilled in theart that additions, modifications, substitutions and deletions notspecifically described may be made without departing from the spirit andscope of the invention defined in the appended claims.

What is claimed is:
 1. A process for treating lead contaminated soils tostabilize leachable lead contained therein, said process comprising thesteps of:mixing a contaminated soil containing leachable lead with asulfate compound having at least one sulfate ion for reacting with saidleachable lead to produce a first mixture, said first mixture containinga substantially insoluble lead compound or mineral species; and mixingsaid first mixture with a phosphate reagent having at least onephosphate ion for reacting with leachable lead remaining in said firstmixture to produce a second mixture, said second mixture containing asubstantially insoluble lead compound or mineral species; curing saidsecond mixture for a period of time; wherein said soil so treated issubstantially solid in form at the end of curing, the concentration ofleachable lead is decreased below 5.0 mg/l, the volume of saidcontaminated soil is reduced as a result of treatment and curing, and nosecondary waste streams are generated.
 2. The process of claim 1,wherein said sulfate compound is selected from the group consisting ofcalcium sulfate, gypsum, sulfuric acid and alum.
 3. The process of claim1, wherein said sulfate compound is supplied in the form of a dry powderhomogeneously mixed with said contaminated soil.
 4. The process of claim1, wherein said sulfate compound is supplied in the form of a dry powderhomogeneously mixed with said contaminated soil.
 5. The process of claim1, wherein said sulfate compound is supplied in the form of a liquidhomogeneously mixed with said contaminated soil.
 6. The process of claim2, wherein said sulfate compound is supplied in the form of a liquidhomogeneously mixed with said contaminated soil.
 7. The process of claim1, wherein said phosphate reagent is selected from the group consistingof phosphoric acid, mono-, di- and tri-basic phosphates.
 8. The processof claim 1, wherein said phosphate reagent is supplied as an aqueoussolution.
 9. The process of claim 1, wherein said phosphate reagent issupplied in the form of a solid from the group consisting of mono-, di-and tri-basic phosphates.
 10. The process of claim 1, wherein theleachable lead is converted to superhard phosphates andphosphate-sulfate mixed mineral crystals, calcium-substitutedanglesites, anglesites and pyromorphites.
 11. The process of claim 1,wherein the sulfate compound is employed in an amount of up to about 30percent of the weight of the contaminated soil being treated.
 12. Theprocess of claim 1, wherein the phosphate reagent is employed in anamount of up to about 30 percent of the weight of the contaminated soilbeing treated.
 13. The process of claim 1, wherein the contaminated soilis permitted to cure for 3 to 5 hours.
 14. The process of claim 1,wherein said contaminated soil has a moisture content of from about 10to about 40 percent.
 15. The process of claim 1, wherein said step ofcuring lasts for a period of 3 to 5 hours.
 16. A process for treatingcontaminated soils to stabilize leachable lead contained therein, saidprocess comprising the steps of:mixing a contaminated soil containingleachable lead with gypsum to produce a first mixture, said firstmixture containing a substantially insoluble lead compound of mineralspecies; and mixing said first mixture with phosphoric acid for reactingwith leachable lead remaining in said first mixture to produce a secondmixture containing a substantially insoluble lead compound or mineralspecies; curing said second mixture for a period of time; wherein, thesoil so treated is substantially solid in form at the end of curing, theconcentration of leachable lead is decreased below 5.0 mg/l, the volumeof said contaminated soil is reduced as a result of treatment andcuring, and no secondary waste streams are generated.
 17. The process ofclaim 16, wherein the gypsum is employed in an amount of up to about 30percent of the weight of said contaminated soil being treated.
 18. Theprocess of claim 16, wherein the phosphoric acid is employed in anamount of up to about 30 percent of the weight of said contaminated soilbeing treated.
 19. The process of claim 16, wherein said contaminatedsoil has a moisture content of from about 10 to about 40 percent byweight.
 20. The process of claim 16, wherein said step of curing lastsfor a period of from 3 to 5 hours.
 21. An in-situ process for treatinglead contaminated soils to stabilize leachable lead contained therein,said process comprising the steps of:mixing a contaminated soilcontaining leachable lead with a sulfate compound having at least onesulfate ion for reacting with said leachable lead to produce a firstmixture, said first mixture containing a substantially insoluble leadcompound or mineral species; and mixing said first mixture with aphosphate reagent having at least one phosphate ion for reacting withleachable lead remaining in said first mixture to produce a secondmixture, said second mixture containing a substantially insoluble leadcompound or mineral species; curing said second mixture for a period oftime; wherein the soil so treated is substantially solid in form at theend of curing, the concentration of leachable lead is decreased below5.0 mg/l, the volume of said contaminated soil is reduced as a result oftreatment and curing, and no secondary waste streams are generated. 22.The process of claim 21, wherein said sulfate compound is selected fromthe group consisting of calcium sulfate, gypsum, sulfuric acid and alum.23. The process of claim 21, wherein said sulfate compound is suppliedin the form of a dry powder homogeneously mixed with said contaminatedsoil.
 24. The process of claim 22, wherein said sulfate compound issupplied in the form of a dry powder homogeneously mixed with saidcontaminated
 25. The process of claim 21, wherein said sulfate compoundis supplied in the form of a liquid homogeneously mixed with saidcontaminated soil.
 26. The process of claim 22, wherein said sulfatecompound is supplied in the form of a liquid homogeneously mixed withsaid contaminated soil.
 27. The process of claim 21, wherein saidphosphate reagent is selected from the group consisting of phosphoricacid, mono-, di- and tri-basic phosphates.
 28. The process of claim 21,wherein said phosphate reagent is supplied as an aqueous solution. 29.The process of claim 21, wherein said phosphate reagent is supplied inthe form of a solid from the group consisting of mono-, di- andtri-basic phosphates.
 30. The process of claim 21, wherein the leachablelead is converted to superhard phosphates and phosphate-sulfate mixedmineral crystals, calcium-substituted anglesites, anglesites andpyromorphites.